Anti-rattle engine balancer which drives associated oil pump

Abstract

A Lanchester type engine balancer avoids rattle of gears connecting counterrotating balance shafts by minimizing inertia through limiting diameters of the counterweight envelopes, timing gears and bearing journals of the balance shafts and by driving an accessory, such as an oil pump from the driven balance shaft. Gear lash is controlled by using a cast iron housing with select fitting of steel gears. Also maximum gear pitch diameter runout is oriented in assembly opposite the counterweights of the respective balance shafts to minimize a change in lash caused by shaft runout due to the eccentric load of the counterweights during operation.

What is claimed is: 
     
       1. An engine balancer having a housing, a pair of first and second balance shafts rotatably carried in the housing on laterally spaced parallel axes, means for connecting the first balance shaft with the crankshaft of an associated engine for rotation in predetermined timed relation therewith whereby the first balance shaft rotates at a speed determined by the crankshaft, a pair of gears connecting the first balance shaft with the second balance shaft for driving the second balance shaft in counterrotation at a speed equal to the speed of the first balance shaft, the balance shafts including counterweights laterally offset from their respective shaft axes and timed to cause when rotated a cyclic shaking force, journals on the balance shafts and engaging bearings in the housing for supporting the balance shafts, wherein the shaft journals are of smaller diameter than envelopes traced by rotation of the counterweights, the counterweights are longer than the diameters of the counterweight envelopes, and the shaft connecting gears are only slightly larger in diameter than the counterweight envelopes,   wherein an oil pump carried by the housing is driven by the second balance shaft to apply rattle reducing load to the shaft connecting gears,   wherein the housing has at least two sections with a parting line intersecting the balance shaft journal bearings to permit the diameter of the bearing journals to be minimized,   wherein the gear, counterweight and bearing journal diameters are sufficiently small that the polar moment of inertia of the second balance shaft times the maximum angular acceleration of the second balance shaft during engine idle operation does not exceed the drag torque acting thereon, and   wherein the maximum pitch diameter runout of the shaft connecting gears is oriented diametrically opposite to the center of mass of the counterweights of their respective balance shafts.